Post-ischemic RSR13 amplifies the effect of dizocilpine on outcome from transient focal cerebral ischemia in the rat

MK-801 attenuates lesion expansion following acute brain injury in rats: a meta-analysis

OBJECTIVE:

To evaluate the efficacy and safety of MK-801 and its effect on lesion volume in rat models of acute brain injury.

DATA SOURCES:

Key terms were “stroke”, “brain diseases”, “brain injuries”, “brain hemorrhage, traumatic”, “acute brain injury”, “dizocilpine maleate”, “dizocilpine”, “MK-801”, “MK801”, “rat”, “rats”, “rattus” and “murine”. PubMed, Cochrane library, EMBASE, the China National Knowledge Infrastructure, WanFang database, the VIP Journal Integration Platform (VJIP) and SinoMed databases were searched from their inception dates to March 2018.

DATA SELECTION:

Studies were selected if they reported the effects of MK-801 in experimental acute brain injury. Two investigators independently conducted literature screening, data extraction, and methodological quality assessments.

OUTCOME MEASURES:

The primary outcomes included lesion volume and brain edema. The secondary outcomes included behavioral assessments with the Bederson neurological grading system and the water maze test 24 hours after brain injury.

RESULTS:

A total of 52 studies with 2530 samples were included in the systematic review. Seventeen of these studies had a high methodological quality. Overall, the lesion volume (34 studies, n = 966, MD = −58.31, 95% CI: −66.55 to −50.07; P < 0.00001) and degree of cerebral edema (5 studies, n = 75, MD = −1.21, 95% CI: −1.50 to −0.91; P < 0.00001) were significantly decreased in the MK-801 group compared with the control group. MK-801 improved spatial cognition assessed with the water maze test (2 studies, n = 60, MD = −10.88, 95% CI: −20.75 to −1.00; P = 0.03) and neurological function 24 hours after brain injury (11 studies, n = 335, MD = −1.04, 95% CI: −1.47 to −0.60; P < 0.00001). Subgroup analysis suggested an association of reduction in lesion volume with various injury models (34 studies, n = 966, MD = −58.31, 95% CI: −66.55 to −50.07; P = 0.004). Further network analysis showed that 0–1 mg/kg MK-801 may be the optimal dose for treatment in the middle cerebral artery occlusion animal model.

CONCLUSION:

MK-801 effectively reduces brain lesion volume and the degree of cerebral edema in rat models of experimental acute brain injury, providing a good neuroprotective effect. Additionally, MK-801 has a good safety profile, and its mechanism of action is well known. Thus, MK-801 may be suitable for future clinical trials and applications.

Neuroprotection during cardiac surgery

Cardiac surgery continues to be associated with significant adverse cerebral outcomes, ranging from stroke to cognitive decline. The underlying mechanism of the associated cerebral injury is incompletely understood but is believed to be primarily caused by cerebral embolism and hypoperfusion, exacerbated by ischemia/reperfusion injury. Extensive research has been undertaken in an attempt to minimize the incidence of perioperative cerebral injury, and both pharmacological and nonpharmacological strategies have been investigated. Although many agents demonstrated promise in preclinical studies, there is currently insufficient evidence from clinical trials to recommend the routine administration of any pharmacological agents for neuroprotection during cardiac surgery. The nonpharmacological strategies that can be recommended on the basis of evidence include transesophageal echocardiography and epiaortic ultrasound-guided assessment of the atheromatous ascending aorta with appropriate modification of cannulation, clamping or anastomotic technique and optimal temperature management. Large-scale randomized controlled trials are still required to address further the issues of optimal pH management, glycemic control, blood pressure management and hematocrit during cardiopulmonary bypass. Past, present and future directions in the field of neuroprotection in cardiac surgery will be discussed.

Intraischemic Nitrous Oxide Alters Neither Neurologic Nor Histologic Outcome: A Comparison with Dizocilpine

N-Methyl-D-aspartate receptor antagonism contributes to the anesthetic action of nitrous oxide (N(2)O). We examined the effects of the N-methyl-D-aspartate antagonists N(2)O and dizocilpine on outcome from filament occlusion of the middle cerebral artery (MCAO). Rats breathed 70% nitrogen/30% oxygen or 70% N(2)O/30% oxygen during MCAO. A third group breathed 70% nitrogen/30% oxygen and was given dizocilpine (0.25 mg/kg IV). After 75 min of MCAO, the rats recovered for 3 or 14 days. Pericranial temperature was maintained at 37.5 degrees C +/- 0.2 degrees C during ischemia and for 20 h postischemia. N(2)O did not alter neurologic scores at 3 days (N(2)O, 21 +/- 6; nitrogen, 22 +/- 8; P = 0.95; 0 = normal; 48 = maximal deficit; mean +/- sd; n = 15) or 14 days (N(2)O, 13 +/- 6; nitrogen, 12 +/- 6; P = 0.93; n = 15-16) postischemia. N(2)O had no effect on infarct size at 3 days (N(2)O, 162 +/- 45 mm(3); nitrogen, 162 +/- 61 mm(3); P > 0.99) or 14 days (N(2)O, 147 +/- 56 mm(3); nitrogen, 151 +/- 62 mm(3); P = 0.99) postischemia. Dizocilpine treatment caused smaller infarcts (3 days: 66 +/- 49 mm(3), P < 0.0001 versus nitrogen; 14 days: 84 +/- 50 mm(3), P < 0.006 versus nitrogen) and reduced the neurologic deficit (3 days: 10 +/- 10, P = 0.002 versus nitrogen; 14 days: 6 +/- 7, P = 0.006 versus nitrogen). N(2)O (70%) had no effect on either behavioral or histologic outcome from transient focal cerebral ischemia when compared with results in rats breathing 70% nitrogen. These results indicate that normobaric N(2)O does not alter the response of rat brain to a focal ischemic insult.

Tongue protrusion: a simple test for neurological recovery in rats following focal cerebral ischemia

A simple tongue protrusion (TP) test is described for rats following focal ischemia induced by middle cerebral artery occlusion (MCAO). MCAO resulted in a dramatic decrease in TP that correlated with a concomitant decline in neurological performance in standard 5- and 20-point tests and deficits in performance in the Morris water maze and the accelerating rotarod. TP values also correlated with infarct size at 7 and 24 days following MCAO. This simple and inexpensive test, that monitors the ability of rats to lick food out of a glass tube, is easily administered, can be administered frequently without changing baseline performance, is not susceptible to behavioral compensation and should not interfere with other tests used concurrently to evaluate neurological deficit. The TP test may, therefore, serve as a useful addition to the battery of tests commonly used to assess neurological damage in rats, particularly in models of stroke.

Increasing P(50) does not improve DO(2CRIT) or systemic VO(2) in severe anemia

Reducing the hemolobin (Hb)-O(2) binding affinity facilitates O(2) unloading from Hb, potentially increasing tissue mitochondrial O(2) availability. We hypothesized that a reduction of Hb-O(2) affinity would increase O(2) extraction when tissues are O(2) supply dependent, reducing the threshold of critical O(2) delivery (DO(2 CRIT)). We investigated the effects of increased O(2) tension at which Hb is 50% saturated (P(50)) on systemic O(2) uptake (VO(2) (SYS)), DO(2 CRIT), lactate production, and acid-base balance during isovolemic hemodilution in conscious rats. After infusion of RSR13, an allosteric modifier of Hb, P(50) increased from 36.6 +/- 0.3 to 48.3 +/- 0.6 but remained unchanged at 35.4 +/- 0.8 mmHg after saline (control, CON). Arterial O(2) saturations were equivalent between RSR13 and saline groups, but venous PO(2) was higher and venous O(2) saturation was lower after RSR13. Convective O(2) delivery progressively declined during hemodilution reaching the DO(2 CRIT) at 3.4 +/- 0.8 ml x min(-1) x 100 g(-1) (CON) and 3.6 +/- 0.6 ml x min(-1) x 100 g(-1) (RSR13). At Hb of 8.1 g/l VO(2) (SYS) started to decrease (CON: 1.9 +/- 0.1; RSR13: 1.8 +/- 0.2 ml x min(-1) x 100 g(-1)) and fell to 0.8 +/- 0.2 (CON) and 0.7 +/- 0.2 ml x min(-1). 100 g(-1) (RSR13). Arterial lactate was lower in RSR13-treated than in control animals when animals were O(2) supply dependent. The decrease in base excess, arterial pH, and bicarbonate during O(2) supply dependence was significantly less after RSR13 than after saline. These findings demonstrate that during O(2) supply dependence caused by severe anemia, reducing Hb-O(2) binding affinity does not affect VO(2) (SYS) or DO(2 CRIT) but appears to have beneficial effects on oxidative metabolism and acid base balance.

Pharmacological correction of hypothermic P(50) shift does not alter outcome from focal cerebral ischemia in rats

Hypothermia decreases the arterial PO(2) at which hemoglobin is 50% saturated (P(50)), increasing hemoglobin O(2)-binding affinity. We used RSR13, a synthetic allosteric modifier of hemoglobin that increases P(50), to study the role of altered hemoglobin O(2)-binding affinity in mild hypothermic neuroprotection. RSR13 (150 mg/kg iv) restored P(50) to normothermic values. Rats underwent 70 min of middle cerebral artery occlusion (MCAO) at 30.0, 34.0, or 37.5 degrees C with hemoglobin saturation held at 98-100%. The 34.0 degrees C group received RSR13 or vehicle before ischemia. After 7 days of recovery, infarct volumes were reduced in all hypothermic groups, without evidence of a detrimental effect on infarct size or neurological score as a result of P(50) correction. To examine for a beneficial effect of P(50) correction, ischemia duration was increased to 120 min in rats maintained at 34.0 degrees C. Correction of P(50) by RSR13 did not alter cerebral infarct sizes or neurological scores. The decrease in P(50), caused by mild hypothermia, could not be associated with infarct size or neurological deficit resulting from ischemic brain hypoxia in rats.

Intracerebral adenosine infusion improves neurological outcome after transient focal ischemia in rats

Second Institute of New Drug Research, Otsuka Pharmaceutical Co., Ltd., Tokushima, Japan In order to elucidate the role of adenosine in brain ischemia, the possible protective effects of adenosine on ischemic brain injury were investigated in a rat model of brain ischemia both in vitro and in vivo. Exogenous adenosine dose-dependently rescued cortical neuronal cells from injury after glucose deprivation in vitro. Adenosine (1 mM) also significantly reduced hypoglycemia/hypoxia-induced glutamate release from the hippocampal slice. In a rat model of transient middle cerebral artery occlusion (MCAO), extracellular adenosine concentration was increased immediately after occlusion, and then returned to the baseline by 30 min after reperfusion. Adenosine infusion through a microdialysis probe into the ipsilateral striatum (1 mM adenosine, 2 microl min(-1), total 4.5 h from the occlusion to 3 h after reperfusion) showed a significant improvement in the neurological outcome, and about 25% reduction of infarct volume, although the effect did not reach statistical significance, compared with the vehicle-treated group at 20 h after 90 min of MCAO. These results demonstrated the neuroprotective effect of adenosine against ischemic brain injury both in vitro and in vivo, suggesting the possible therapeutic application of adenosine regulating agents, which inhibit adenosine uptake or metabolism to enhance or maintain extracellular endogenous adenosine levels, for stroke treatment.

RSR13 e modificação alostérica da afinidade hemoglobina-oxigênio: abuso entre atletas

O ácido metilpropiônico (RSR13) é um modificador alostérico da hemoglobina, com a qual se liga de forma não-covalente, diminuindo sua afinidade pelo oxigênio de modo dose-dependente e, conseqüentemente, aumentando a oxigenação periférica. O objetivo deste artigo é apresentar brevemente as evidências científicas acerca das características farmacológicas e funcionais, indicações médicas e efeitos adversos do uso do RSR13 por atletas, a mais recente alternativa de aumento artificial do desempenho. Estudos experimentais preliminares verificaram algum efeito positivo do RSR13 sobre a recuperação do miocárdio isquêmico e sobre a extensão da isquemia cerebral, mas as principais indicações estudadas atualmente são a cirurgia com hipotermia e cardioplegia durante circulação extracorpórea e o uso como agente coadjuvante potenciador da radioterapia para certos tumores sólidos. Somente um estudo em modelo canino mostrou aumento do consumo máximo de oxigênio em músculo isolado, não existindo evidências de que o RSR13 possa efetivamente melhorar o desempenho em humanos. Em realidade, já foram descritos efeitos adversos, como diminuição da perfusão sanguínea, elevação da pressão arterial e diminuição da função renal. Antecipando o potencial aumento da utilização do RSR13 por atletas, métodos já foram desenvolvidos para sua detecção em amostras de urina humana.